1. Field of the Invention
The present invention relates to an acceleration sensing device and a manufacturing method of the acceleration sensing device, in particular, to a miniaturized acceleration sensing device and a manufacturing method of the miniaturized acceleration sensing device. This is a counterpart of and claims priority to Japanese Patent Application No. 2004-254812 filed on Sep. 1, 2004, which is herein incorporated by reference.
2. Description of the Related Art
A manufacturing technology for tiny structures having dimensions of several hundred micrometers has been developed by applying a semiconductor fine processing technology. The manufacturing technology is just beginning to be applied to various sensors, optical switching devices in a photonic art and radio-frequency radiation devices. Since the tiny structures such as those devices are manufactured by an established semiconductor manufacturing processes, the tiny structures may be formed on a single chip. The device which includes the above-described tiny structures and systems with specific functions is called a Micro-Electrical-Mechanical-Systems (MEMS) device or a Micro-System-Technology (MIST) device. The MEMS devices include an acceleration sensing device, for example as shown in a Patent Document 1 (Japanese Patent Publication Laid-open No. Hei 11-135804).
The piezo acceleration sensing device described in the Patent Document 1 has a frame member which includes a center part and flexible parts. Each of the flexible parts extends between the center part and a portion of an inside surface of the frame member. The acceleration sensing device also has a sensing member swingably supported by the center part. The acceleration sensing device still also has a support member which supports a lower surface of the frame member and surrounds a periphery of the sensing member through a space. Since the sensing member moves by an external force or an external stress, the sensing member is also called a movable sensing member. The movable sensing member and the flexible parts are integrally configured so as to have the tiny structure. The flexible parts have small thicknesses and narrow widths. The sensing device which has configurations as described above a packaged device.
FIG. 1A is a schematic top view for describing an acceleration sensing device 100 in the related art. FIG. 1B is a schematic sectional view along a dashed line A-A′ of the acceleration sensing device 100 in FIG. 1A. In FIG. 1A, an after-described protective covering member is omitted so that internal configurations of the acceleration sensing device 100 can be shown. The acceleration sensing device 100 has an acceleration sensing chip 110. The acceleration sensing chip 110 has a plurality of electrode pads 112. The acceleration sensing chip 110 outputs signals through the electrode pads 112 or receives input signals through the electrode pads 112. The acceleration sensing chip 110 includes a moving sensing member 114 which mechanically operates. The acceleration sensing chip 110 has a sealing substrate 116 which covers the movable sensing member 114 and limits an operation of the movable sensing member 114. The sealing substrate 116 is mounted on a base substrate 120 through an adhesive film 122. The acceleration sensing device 100 also has the protective covering member 130 which covers the acceleration sensing chip 110 and the sealing substrate 116. The protective covering member 130 is disposed on the base substrate 120 so that a rim of the protective covering member 130 joins the base substrate 120. The protective covering member 130 configures an interspace 140 in which the acceleration sensing chip 110 is disposed. The base substrate 120 has a plurality of external terminals 150 arranged at a periphery of the base substrate 120. The external terminals 150 extend from the interspace 140 toward outside of the protective covering member 130. The electrode pads 112 of the acceleration sensing chip 110 are electrically coupled with the external terminals 150 in the interspace 140 through a plurality of bonding wires 160.
In the above-described acceleration sensing device 100, the acceleration sensing chip 110 and the external terminals 150 are electrically coupled with each other through the bonding wires 160, and furthermore the protective covering member 130 covers not only the acceleration sensing chip 110 but also the bonding wires 160. Therefore, it is difficult to seal the acceleration sensing chip 110 and the bonding wires 160 by transfer molding method or a potting method using liquid resin. As a result, it may be difficult to miniaturize the acceleration sensing device 100. Also, in a manufacturing method of the above-described acceleration sensing device 100, each of the acceleration sensing chips 110 is sealed by the protective covering member 130 after a wafer is diced, to obtain each of the acceleration sensing devices 110. That is, each of the acceleration sensing chips 110 may be sealed with waste materials of the wafer formed during the dicing process adhered to a periphery of the movable sensing member 114. Therefore, the movable sensing member 114 may not operate properly because of the waste materials.